In a connection-oriented communication network, the transfer of information between two end-users is accomplished by network functions that select and allocate network resources along an acceptable path. The logical association between the communicating end-users is referred to as a call. The chain of associated network resources that support the call is referred to as a connection. Connection management is a network function that is responsible for setting up, maintaining, and taking down connections. Each call request is issued with a set of quality of service (QOS) requirements that govern the resource allocation for the desired connection.
Conventional allocation of network resources for connection management is by and large static. A fixed level of quality of service, specified by the user, is to be matched at connection setup for a call, and the same must be maintained by best efforts throughout the duration of the call. Certain performance parameters, such as throughput and delay, are negotiated to determine their respective agreed values. The same agreed values must ideally be met as long as the call is active. When the need arises such that the agreed QOS must be adjusted, the call and supporting connection are taken down and the call establishment process is started anew.
Static allocation of network resources is inefficient, and is clearly inadequate for a dynamic networking environment where the user requirements and the quality characteristics of network resources are not static. Resources on a link may degrade in performance, and yet the link is still regarded as operational because appropriate performance thresholds are not exceeded. For example, when a leased facility serving as an internodal link is switched from a non-satellite link to a satellite link, the delay performance for a connection using the link may be degraded considerably. On a satellite link, weather changes can cause accuracy values to fluctuate so much that the accuracy performance for a connection using the link may be degraded considerably.
With user demands that vary with the time of the day, and the bursty nature of many traffic types, a network is prone to sporadic heavy loads. A connection that is established or reestablished when the network is heavily loaded tends to receive a less than a desirable QOS level. This may be acceptable for connections that do not last a long time. But for permanent connections, this is highly undesirable.
With the introduction of ISDN (Integrated Services Digital Network), communication networks supporting diverse QOS have become a reality. Due to different traffic characteristics and QOS requirements, it has become necessary to allow the users to negotiate the values of certain performance parameters. One of the biggest challenges for today's integrated networks is to guarantee the negotiated QOS in a dynamic network environment.
In ISDN, each negotiable performance parameter is assigned an acceptable value. A user who wishes to use values that are more desirable than the acceptable values may configure a requested value for each of the parameters. In a parameter negotiation, an agreed value is determined so that it is within the range between the acceptable value and the requested value. The agreed value is made available by the network at call establishment time, but not guaranteed for the duration of the connection. The agreed value may not be adjusted within the duration of the call.
In-call renegotiation of performance parameters for dynamic allocation of network resources is known. For example, the user whose demand for network resources is changing may send a renegotiation request to the network. If sufficient resources are available to accommodate the request, the performance adjustment is permitted, with possible rerouting of the connection required. Otherwise, the request is rejected. After such a denial, the user has to wait for a random length of time before issuing another request. The drawback of this approach is that it involves in-call interactions between the user and the network. Moreover, it does not address the problem of quality of service falling out of match as the allocated resources degrade in performance.
In the prior art, there are preemptive network resource allocation strategies based on disruptive retrieval of network resources that have already been allocated to existing calls in order to accommodate new calls of greater importance. Typically, a call that is preempted is either terminated prematurely, or considered for re-establishment. In the attempt to reestablish a preempted call, if the previously agreed performance values could not be satisfied, the call is also terminated.
Due to occasional changes in transmission facilities or service requirements, the QOS offered at call establishment time may be degraded. To guarantee the negotiated performance values over the entire duration of a connection, the network must monitor changes in the network, and take timely and appropriate actions whenever QOS degradation is detected. Transmission facilities may at times be degraded beyond operational. The network must also provide the capability to reroute connections that are affected. In a network where call preemption is allowed, the network must minimize such disruption by rerouting preempted calls.
Thus, there is a need for a system and method that addresses the problem of managing connections, in a connection-oriented integrated communication network, to maintain acceptable QOS for the entire duration of each connection, to make QOS improvements whenever it is possible, as well as to recover from connection failures and preemption.